The present invention relates to a reset control technology of a data processor, and in particular to a technology for sharing one external reset terminal for the input and output of a reset signal, e.g., a technology effective if applied to a keyboard of a PC (personal computer) and a power-supply control microcomputer thereof.
A power-on/low voltage detection circuit (POR/LVD detection circuit) that detects the turn-on of a power supply voltage and a reduction in the level of the power supply voltage as reset factors respectively is on-chipped to a data processor. Consequently, the data processor is capable of performing initialization autonomously with respect to the turn-on of the power supply voltage and the reduction in the level of the power supply voltage without depending on a reset IC for achieving a similar function at the outside. Each of reset signals generated by other on-chip circuits starting with the POR/LVD detection circuit is outputted from its corresponding external terminal, whereby it can be used as a reset signal for initializing each of other LSIs.
The following patent document 1 has described that a microcomputer (micon IC) is used as a high-functionality reset IC. That is, the micon IC has a reset control means and is provided with the function of detecting on/off of a power supply circuit of a CPU target for control, performing a reset operation on the CPU, based on a command issued from the CPU when the power supply circuit is in an on state, bringing the power supply circuit of the CPU to an on state when the power supply circuit is in an off state and then resetting the CPU automatically.    [Patent document 1] Japanese Unexamined Patent Publication No. Hei 10 (1998)-312227